The theft of automobiles and of property from parked automobiles represents one of the more significant areas of criminal activity. As the use of automobiles has increased, so has the incidence of thefts involving automobiles. The economic impact of automobile larceny is reflected in part in the increased rates of automobile insurance, and the disproportionate number of automobile accidents involving stolen automobiles in which the unauthorized drivers are often minors. It is also a common practice for thieves to forcibly enter a parked automobile to pilfer articles such as luggage and radios, and in case of an automobile belonging to a doctor, as indicated by the license plate, medical bags hopefully, in the eyes of the thief, containing narcotics.
The provision of an alarm actuated upon the unauthorized opening of the car door of the automobile, or the operation of any electrically controlled device in the automobile, constitutes an effective deterrent against thefts of this type. The sound of a wailing siren or horn almost certainly upsets the plans of the would-be car thief, and quickly attracts the attention of the police and others.
Alarms of this type have been proposed and are in widespread use on trucks carrying large quantities of goods often having considerable value. The warning alarm, which has as its main object the protection of goods, generally comprises a plurality of switches which are responsive to the unauthorized opening of doors or the like, and which when actuated, energize a relay to in turn energize a warning device such as a siren. Apparatus of this type requires the installation of a large number of components in the vehicle, such as the switches, relays, etc., and as a result, the cost of purchasing and installing such apparatus is generally high. Owners and operators of trucks are usually willing and able to pay this because the potential saving in insurance premiums, and the increased protection of their customers' products and the accompanying customer good will, make the cost of a warning device of this type well worthwhile.
The acceptance and use of such warning devices by owners of automobiles has, however, been greatly limited, largely as a result of the high initial purchase cost and the difficulty of installation. The known alarm devices adapted for use in automobiles have the further drawback of being not always reliable, and in that the failure of the device often results in the failure of the automobile's electrical system.
More recently, vehicle alarm systems have been developed which are directly responsive to the energization of a load device such as a dome light resulting from unauthorized entry of the vehicle. In some systems, a current sensitive device is interposed between the battery and the load device and is effective upon energization of that load device (by the opening of a door or trunk) to energize a latching relay or switch, thereby to activate the alarm. Systems of this type, while they are somewhat less complex and expensive than the systems mentioned above, nevertheless have several drawbacks. For example, they are difficult to install because the accessory leads must be opened in order to install the one or more current sensitive devices. Moreover, a failure of the thus installed current sensing device may produce a failure of one or more load devices or in some cases failure of the entire electrical system of the vehicle.
A second category of system of this type is sensitive to the voltage level at the battery and is adapted to detect unauthorized entry by sensing a voltage dip at the battery terminals resulting from the energization of a load device and is adapted to activate the alarm in response thereto. While these systems are easier to install, they are frequently subject to false alarms. Thus, because the sensing circuit is responsive only to battery voltage magnitude, it will respond to all fluctuations, including those not associated with unauthorized entry. As a result, systems of this type are often activated by such events as nearby radio transmission, extremes of temperature, changes within the battery itself, and even the winding of a conventional automobile clock.
In my aforementioned U.S. Pat. No. 3,671,934, I disclose a vehicle alarm circuit which is responsive only to the rate-of-change of voltage at the battery terminals. Accordingly, that circuit discriminates between resistive loads normally associated with unauthorized use of the vehicle and inductive loads, resulting from extraneous events. That alarm system, accordingly, represents a substantial improvement over prior art vehicle warning devices in that it combines exceptional reliability at low cost with relatively easy installation.
All known vehicle alarm systems, including my most recent "rate-of-change of battery voltage" sensing system described above, are provided with manually actuated means for arming the alarm, typically in the form of a simple switch. The switch may be accessible from the outside of the vehicle, in which case it is key actuated, or it may be located in a suitable location within the vehicle. In the latter case, time delay means may be provided to allow entrance by the authorized user without activating the alarm. In either case, however, the alarm circuit must be completely deactivated prior to authorized use of the vehicle and will not be effective upon the driver's leaving the vehicle unless reactivated at that time. Stated in other terms, in all prior art vehicle warning systems the choice of arming the alarm circuit is left to the driver. The presumed necessity of this feature has in the past been perhaps the major obstance to the effectiveness of vehicle alarm systems. Thus, the most sophisticated warning system is completely useless if the driver does not arm it. Consequently, while prior art vehicle alarm systems are today fairly widespread, drivers quite often inadvertently forget to arm them or consciously forego arming in situations in which they (normally unjustifiably) feel the chance of unauthorized entry is minimal. As a result, insurance companies place very little stock in such systems and their widespread use has not been effective in lowering high insurance rates.
The above mentioned problems have been satisfactorily solved by the alarm system described in my aforementioned copending application Ser. No. 217,181, which combines a battery voltage "rate-of-change" sensor with a unique automatic arming system controlled by the ignition switch of the vehicle. Briefly, that system employs a unique pulse generator circuit adapted to energize an alarm device (normally the horn) in pulse fashion in response to an alarm signal provided by the rate-of-change sensor. That alarm signal is effective to trigger a latching circuit connected in operative circuit arrangement with the pulse generator circuit. The pulse generator is designed with a built-in initial capacitive time delay, so that unlatching of the latch circuit within such initial delay effectively prevents energization of the alarm. Means are provided for unlatching the latching circuit when the ignition switch is turned, by means of the ignition key, to the ignition position. Accordingly, the aforementioned delay provided by the pulse generator circuit provides sufficient time to enable the driver to enter and start the vehicle thereby temporarily disabling the alarm.
In addition, means are provided, again responsive to the ignition switch, for inhibiting the sensing circuit when the vehicle is being operated, thereby to prevent momentary alarm actuation in response to the energization of load devices such as lights, cigarette lighter, radio, etc. That inhibiting circuit is provided with means to maintain the sensing circuit insensitive to battery voltage fluctuations for a predetermined time after the ignition switch is turned to the off position, thereby to afford an exit delay sufficient to allow the driver to leave the vehicle with activating the alarm.
The pulse generating circuit, however, remains armed unless positively disarmed by the driver. For this latter purpose there are provided pulse inhibit and permanent disarm circuits operatively connected to the pulse generator circuit, the combined effect of which is to disarm the circuit only when the ignition switch is turned to the accessory position and maintained in that position for a predetermined time. After such predetermined interval, if the ignition switch is turned off, the alarm remains disabled, the pulse generator circuit having been shorted out. However, the pulse generator circuit is automatically returned to its initial enabled condition when the ignition switch is next turned to the start position. As a result, when the ignition switch is thereafter turned off, the circuit is automatically armed after the expiration of the exit delay. The aforementioned arming circuit, including pulse inhibit and permanent disarm subcircuits, is effective to provide automatic arming but this feature is attained with considerable complexity in the circuitry which increases expense.
Nevertheless, the above described alarm system represents a major advance in vehicle warning systems as a result of its completely automatic operation including automatic arming and entrance and exit delays. Notwithstanding its unique and desirable features, however, this system is still deficient in several additional important respects.
First, it will be appreciated that a rate-of-change of battery voltage sensor is limited in its effective protection to those modes of entry and/or tampering which involve the energization of a resistive load device. Thus, while the alarm will respond to normal entry by the doors or trunk (with which courtesy lights are normally associated), special provision must be made, for example, for the hood, which normally does not come equipped with a lamp. In addition, the battery voltage sensor is not effective to detect forcible entry through other areas of the vehicle such as by breaking a window. In this regard, some automobiles now come originally equipped with a protective loop or other protective circuitry adapted to be operatively connected to an alarm system for sensing attack on the thus protected elements of the vehicle.
Moreover, even if all likely areas of entry and/or tampering are adapted to be sensed, the built-in entrance delay of the aforementioned system will in many cases afford the intruder sufficient time either to abscound with the stolen property (i.e. from the trunk) or to deactivate the entire electrical system of the vehicle, for example, by opening the hood and disconnecting the battery terminals.
A second obvious limitation of my aforementioned system is that there is no way for the authorized driver to disable the alarm on a continuous basis--the system is automatically rearmed after each use of the vehicle unless specifically disarmed. While this feature insures active use of the alarm system, it may become a nuisance under certain conditions--for example where the driver is making several stops for pickup or delivery without leaving the vehicle unattended. It is therefore desirable to provide means for permanently disabling the alarm without, however, compromising the security of the system.
Another source of difficulty in my aforementioned circuit is that once the alarm is initiated, it will continue until shut off with the ignition key. An attempted burglary will generally be thwarted by the alarm in a matter of seconds or at most minutes. Thereafter the continuing of the alarm results in unnecessary noise which at best will drain the vehicle battery and at worst will result in damage to the vehicle by neighbors or police in an effort to stop the alarm. In the past, this problem has been avoided by automatic shutoff systems. However, prior art systems of this type unavoidably compromise the security of the system since the alarm is not automatically rearmed after it has run its course--a second attempt at entry will succeed.
Finally, in all prior art vehicle alarm systems with exit delays, it has been found that the system is too unflexible. For example, the unloading of goods from the vehicle may extend beyond the interval of the exit delay and the subsequent transient resulting from the closing of the door may activate the alarm. Similarly, many vehicles now come equipped with an option which maintains the headlights operative for a period of 3-4 minutes after the ignition has been turned off to illuminate the way. It has been found that in my aforementioned system the transient associated with the automatic shutoff of the headlights after this period may falsely activate the alarm. Accordingly, it is desirable to provide safeguards against alarm activation under these circumstances.
It is a primary object of the present invention to provide a vehicle alarm system having an improved arming circuit which is simple, inexpensive and reliable and provides automatic rearming after each authorized use of the vehicle without any positive action of the driver.
It is another object of the present invention to provide an ignition controlled alarm circuit of the type described including auxiliary manually actuatable control means effective to prevent automatic rearming but ineffective to disarm the system once armed, thereby to provide flexibility without compromising security.
It is yet another object of the present invention to design a vehicle alarm system of the type described including an entrance delay in alarm activation which is conditional upon the mode of entry, said delay being bypassed by unauthorized entry or tampering without opening of the vehicle door.
It is still another object of the present invention to provide an alarm circuit for a vehicle security system including two separate sensing circuits one of which is adapted to sense the energization of a resistive load device and the other of which directly senses tampering and/or entry at specific locations on the vehicle, those circuits being connected in parallel and each being effective to initiate an alarm.
It is yet another object of the present invention to design a vehicle alarm circuit of the type described including an exit delay which is responsive to the condition of the vehicle door.
It is still another object of the present invention to provide a vehicle alarm system of the type described including means to prevent alarm activation in response to an automatic headlight turnoff after the ignition is turned off.
It is still another object of the present invention to design a vehicle alarm system with means to automatically shut off the alarm a predetermined interval after it is initiated, and to automatically rearm the circuit upon such shutoff.
To these ends, the present invention comprises a vehicle alarm system of the general type described in my aforementioned copending application Ser. No. 217,181, with a series of major improvements and additions effective to reduce cost and increase flexibility and reliability of operation. Briefly, that system includes an alarm device operatively connected in series with a relay activated switch, the relay being connected in operative circuit arrangement with a pulse generator circuit adapted upon energization to provide rapid pulse activation of the relay and thus of the alarm device, in a manner similar to that described in the aforementioned copending application.
In a preferred embodiment both the vehicle horn and headlights are utilized as the alarm device, pulsed actuation providing a distinctive audible and visible alarm.
As in the system of my copending application, the pulse generator is actuated by a latching SCR after an inherent entrance delay in response to an alarm signal. That signal, in accordance with the system here disclosed, may be produced by either or both of two independent sensing circuits, one of which is substantially identical to the rate-of-change of battery voltage sensing circuit disclosed in my U.S. Pat. No. 3,671,934. The other sensing circuit is directly coupled to the hood circuit and/or a tamper circuit comprising a closed protective loop provided as original equipment on some late model vehicles. This D.C. coupled sensor circuit, besides activating the aforementioned SCR, also provides a substantially immediate activation of the pulse generator circuit, thereby bypassing the entrance delay. An additional circuit operatively connected to the entrance delay circuit is also effective to bypass the entrance delay when the cause of the alarm is other than the opening of a door. As a result, any tampering with the vehicle in an attempt to deactivate the electrical system or to gain entry other than by opening the door will provide an immediate alarm (if the vehicle doors are securely locked this may be all the protection which is needed). However, the entrance delay provides the authorized user sufficient time within which to enter the vehicle through the door and turn the ignition on. Once this occurs, the pulse generator circuit is immediately disabled preventing alarm activation during operation. At the same time the aforementioned SCR is unlatched by the battery voltage on the accessory line by means of a novel latching/unlatching circuit.
That circuit comprises a depletion mode field effect transistor operatively connected in series with the latching SCR and effective to provide the necessary holding current therefor when the voltage at its gate terminal drops below a predetermined level. That gate terminal is operatively connected to the accessory line of the vehicle which is effective to impress 12 volts thereon upon switching of the ignition switch to either the accessory or ignition position thereby to render that FET nonconductive resulting in an elimination of the holding current necessary to maintain the SCR latched in its conductive condition. Upon disconnection of the accessory line from the battery voltage, the gate terminal of the FET is discharged to ground via an RC network with a large time constant, the time required to discharge that gate terminal below the threshold level constituting a relatively long exit delay.
As in the system described in my copending application, the alarm may be disarmed by turning the ignition switch to the accessory position and leaving it there for a predetermined period. However, in the present system this is accomplished in a much simpler and reliable way. Thus, the accessory line is operatively connected to the gate of a second SCR which when conductive is effective to short out the pulse generator circuit. However, in the ignition position of the ignition switch that SCR is bypassed by a parallel connected conductive transistor so that no current flows through the SCR and when the ignition is turned off the SCR, never having latched, remains nonconductive. If, however, the ignition switch is turned to the accessory position, the gate of the SCR remains energized while the base of the bypass transistor is discharged through an RC network. Once the bypass transistor is turned off (which takes approximately 5 seconds) current flows through the SCR latching same to disable the circuit. Upon subsequent use of the vehicle, the SCR is again unlatched by the bypass transistor.
An additional important feature of the invention is the automatic shutoff circuit which is operatively connected to the output of the pulse generator circuit and to the latching circuit RC network and is effective to charge the gate terminal of the latching FET through the battery in corresponding pulse increments. Upon reaching the threshold level (which may take approximately 5 minutes) the FET is rendered nonconductive unlatching the SCR and terminating the alarm. Thereafter, the gate terminal again discharges to ground rearming the circuit. As a result, the vehicle remains protected even after an attempted theft.
Another new feature of the present alarm system is the provision for a manual switch which, if activated prior to ignition shutoff or when the pulse generator circuit has been temporarily disarmed via the ignition switches as previously described, will permanently prevent the circuit from rearming thereafter until that switch is turned off. That switch is operatively connected to the aforementioned automatic shutdown circuit and is effective to prevent the gate terminal of the latching FET from discharging. The FET is thereafter maintained nonconductive until the switch is turned off regardless of the position of the ignition switch.
Finally, the present alarm system is provided with means to render the battery voltage sensor insensitive to voltage fluctuations while the headlights are on and for a fraction of a second after they are turned off. This feature effectively prevents false alarms in response to automatic headlight shutoff a given interval after the driver has exited the vehicle, as is the case in some late model automobiles.